Vehicles are controlled electronically more and more in recent years. For example, in JP 2004-125061A, a gear shift range changeover operation by a gearshift lever of an automatic transmission is detected by a switch, etc. Based on the detection signal, an electric actuator such as an electric motor is controlled so that a range of a shift range changeover device is changed over to a target range selected or instructed by a driver of a vehicle. This is a shift-by-wire range changeover control system.
Furthermore, in JP 2004-125061A, abnormal operation of a vehicle is prevented at the time of failure of the automatic transmission. That is, an actual shift range of the automatic transmission is detected and the detected range is compared with the target range selected by the driver. The presence/absence of abnormality of the automatic transmission is determined based on whether the detected actual range agrees with the target range. When abnormality is determined, a driving power transfer system from the engine side to the driving wheel side is interrupted, so that the output power of the engine is not transmitted to the driving wheel.
The shift range is changed over to the target range, after the driver makes a target range changeover operation and the motor is driven to effect the changeover. As a result, a range changeover delay is caused in correspondence to a motor drive time from an instruction of the changeover of the target range to a completion of an actual changeover. Therefore, it becomes necessary not to determine the presence/absence of abnormality for a predetermined wait period after the target range is changed over. This predetermined wait period is set longer than a changeover operation delay period in the range changeover device. The presence/absence of abnormality in the automatic transmission is thus determined after the predetermined wait period elapses by checking whether the actual range is the same as the target range.
In such abnormality determination, a detection delay is caused until the abnormality is detected after the target range is changed over. This detection delay corresponds to at least a range changeover operation delay time. Therefore, it is impossible to restrict the vehicle from abnormal operation during the abnormality detection delay, when the abnormality actually arises.
Even when the range changeover device operates normally according to a changeover in the target range, an accelerator pedal is sometimes pressed down for engine acceleration before the range changeover to the target range is completed. In this instance, with the previous range before the range changeover, that is, a range which the driver does not want any more, the engine output power may increase and vehicle driving force may increase. Thus, it is likely that the vehicle operates abnormally, although the driver does not expect such an operation.